Various kinds of window coverings exist, wherein a window covering, for example, a plurality of blind slats, in the case of venetian blinds, or some other form of window covering material such as drapery material or the like in certain other kinds of window covering, must be adjusted or controlled from above in various ways.
In particular, venetian blind structures are well known consisting of a head rail supported typically in a window or in an opening. A series of horizontal slats are suspended beneath the head rail. They are carried on what are known in the trade as "ladder tapes" or simply "ladders". In addition, suspension cords, or "raise" cords, pass through openings in the slats, to the lowermost slat. Raising and lowering of the suspension cords permits the slats to be raised and lowered. The ladder tapes are pairs of cords or tapes with spaced apart transverse flexible elements somewhat in the manner of rope ladders. The tapes actually support the weight of the individual slats and separate them from one another. At their upper ends in the head rail, the ladder tapes are secured in such a manner, to a tape control rod, that the tapes on one side of the slats may be wound up, while the tapes on the other side of the slats are unwound. In this way, the slats can be tilted from the horizontal to an almost, but not completely, vertical position and back again. Usually, they can be tilted either way from the horizontal, to provide various effects of light and shade within a room.
In the past, numerous different designs of ladder tape controls have been provided in different makes of blinds. Generally speaking, a transverse control shaft extends along most of the length of the headrail, and is operated by a drive at one end of the head rail. Usually a worm and wheel gear drive is used, operated by means of a wand. In some cases, a direct drive is provided, operated simply by means of an endless chain, driving a sprocket keyed directly to the control shaft.
In whatever manner, some means are provided for rotating the transverse control shaft to and fro through a predetermined arc, usually slightly less than 180 degrees, although a greater rotation may be required depending upon the width of the slots, and the diameter of the shaft.
The vertical cords or tapes of the two ladder tapes were attached in some fashion to the shaft, so that when the shaft was in the mid position, i.e., at about the 90 degree rotational position, the two ladder tapes were of equal length. In this way, the "rungs" of each of the ladder tapes were essentially horizontal, so that the blind slats were horizontal and were thus "open". As the shaft was rotated one way or the other, the rungs then tilted one way or the other, causing tilting of the actual slats in the same fashion.
The actual manner in which the cords were attached to the shaft varied from one manufacturer to another. In order to provide for an adequate degree of tilting movement of the slats themselves, i.e., from a more or less vertical position on one side to a more or less vertical position on the other side, it was desirable to provide some form of drum device on the shaft, to which the two ends of the ladder tapes or cords could be attached. The drum device would usually have a predetermined diameter greater than that of the shaft itself. In this way, partial rotation of the shaft would provide an adequate degree of movement of the cords themselves, so as to produce a complete tilting movement of the slats from one extreme tilt to the other. Obviously, for reasons of economy it was desirable to have a control shaft of a simple economical slender design to take up a minimum of space and use a minimum of material, and yet to have actual tape drums of adequate diameter, to produce a sufficient degree of movement of the cords for the purpose.
Various problems arise in the design of such drum devices. For example, it is necessary that, in some way, the drum be keyed to the shaft so that when the shaft is rotated the two or more drums supporting the two or more sets of ladder tapes or cords will all be rotated in unison. The drums must be held at a predetermined height along the length of the head rail, so as to maintain the blind slats level. Some form of attachment means must be provided for a quick attachment of the cords to the drums, so that during assembly, workers do not have to spend excessive time on insuring that the lengths of cord are equalized as between two or more drums. If there is any inequality in the length of the pairs of cords, then the blind will not hang level.
All of these features must be provided in low cost parts which are simple and economical to manufacture and for which the tooling cost is a minimum, and which are adaptable to blinds of a variety of different sizes.
Another problem that arises in the design of such venetian blinds is the provision of bearings within the head rail to carry the shaft. It is, for example, not uncommon to attempt in some way to associate bearing devices with the drums carrying the cords, so that the assembly on the shafts is simplified. However, not only is it necessary to assemble the bearings and the drums on the shafts, it is also then necessary to place the shaft, with its bearings and drums, on complimentary bearing supports located in the head rail. It is also necessary to do this by such means that the shaft is retained in position in the head rail so that it cannot inadvertently spring upwardly due, for example, to over vigorous rotation of the shaft, by a user.
It must also be borne in mind that the ladder cords or tapes will, in fact, pass through openings in the head rail, downwardly, so as to support the slats below the head rail. Usually the head rail is also made of sheet metal, and any openings will have relatively sharp edges. It is, therefore, desirable to provide some form of anti-friction guide means within the head rail, registering with the holes in the head rail, through which the ladder cords can pass, so that wear on the cords is reduced to a minimum, thereby prolonging the useful life of the blinds.
It will also be remembered that such venetian blinds also have cords for raising and lowering the entire set of horizontal slats. As explained, this is usually achieved by means of what are known as "raise" cords, which pass downwardly through openings in the head rail and downwardly through openings in successive slats, and are fastened at a lower most slat member.
Usually there are two raise cords, and they pass through a frictional cord lock pulley device at one end of the head rail. Pulling on the two cords together will raise the blind, and releasing the two cords from the cord lock will permit the blind to be lowered. Again, it is highly desirable to provide some form of anti-friction guide means in the head rail, for guiding the raise cords, during their movement so as to minimize wear, and thereby prolong the useful life of the blind.
In the past, one of the commonest designs of drum and bearing systems for the ladder cords has been based on a combination of a sleeve of generally thermoplastic material slid on the shaft, and a more or less cylindrical band of sheet metal material clamped around the thermoplastic sleeve. The band of thermoplastic material was formed with struck-out tongues. The ends of the cords could be placed under the tongues which were then squeezed flat, thereby holding the cords in position. However, the design of the bearing supports in the head rail, which were used in combination with this system, provided two spaced-apart closed bearing rings to retain the control rod in position.
The assembly of the control rod into these two bearings each with closed bearing rings presented a tedious problem. A first thermoplastic sleeve with its clamping cord sleeve around it was placed on the control rod. The control rod was then slid through a first one of the bearing rings. A further sleeve was then placed on the control rod with a further cord clamping sleeve on that plastic sleeve, and that was then slid into the second of the bearing rings. When the rod and the various sleeves were then in Position in the bearing rings, the ladder cords could then be led upwardly through openings in the head rail, and wrapped around the drums, hooked under the sheet metal tongues which were then flattened to hold the cords in position. This assembly work required considerable skill and considerable time. If any mistake was made in clamping of one or other of the cords in position, then the blind would never hang level, and it was necessary to send a service man to correct the problem. Not infrequently, one or more of the cords would become loose from having been inadequately clamped underneath such a tongue, again requiring service calls.
The apparatus, therefore, required several different parts some made of thermoplastic and some made of sheet metal, and required a lengthy and complex assembly process, which had to be carried out in a precise order, and with considerable skill exercised at various stages, in order to produce a satisfactory result.
The net result increased the overall cost of the blinds to an unacceptable extent.
Clearly, it would be advantageous to provide a system wherein the drum devices can be assembled on the shaft, independently of the head rail. Advantageously the assembly of the drum devices and the shaft can then be inserted in suitable bearing supports in the head rail, and then finally the cords can be placed in position, adjusted to length easily and readily, and securely clamped, by finger pressure. Preferably all of the parts will be manufactured of thermoplastic material so that special tools for clamping sheet metal parts will not be required, the clamping being achieved simply by a frictional interference fit between two plastic parts clamping the cords.
In addition, advantageously such a system will incorporate anti-friction means for guiding both the ladder cords and also the raise cords, without the provision of additional parts requiring extra assembly operations.
As noted above, while the invention is of particular application to venetian blinds having slats which must be tilted to and fro, it is also of application to other forms of window covering devices.